In order have a reasonably firm contact with road, grooves of a tread of a vehicle tyre need to be reasonable deep. Commonly, for safety reasons, the minimum groove depth is also governed by a national law. Naturally, when a tyre wears, the grooves become shallower. In order to determine the need for changing a tyre, different types of wear indicators may be employed onto the tread of a tyre. For a user, a wear indicator being capable of indicating the groove depth with a numerical value, such as an Arabic numeral, is informative.
An example of such a wear indicator is shown in US2005/0081971. According to that solution, as the tyre wears, different numbers are uncovered at different locations. However, such a wear indicator requires a lot of space from the tyre tread, as each number requires its own position. To reduce the size of the wear indicator, but still maintaining the readability, the document WO2007/102790 discloses a tyre with a wear indicator consisting of seven sipes with different depths. The depth of the sipes is designed in such a way that the appearance of the wear indicator changes from the symbol “8” to the symbol “6” and further to a symbol resembling “4”, when the tyre wears.
A problem with the latter wear indicator is that the blades of the mould for making the sipes of the wear indicator prevent rubber from flowing into the mould, in particular to the inner corners thereof. Moreover, to provide more information to a user, a greater number of different symbols should be expressible with the wear indicator. Increasing the complexity of a mould used for making the wear indicator may involve a mould having a complex shape that is even harder to fill with rubber. The mould for such an indicator should be designed such that the flow of rubber during curing of the tyre is not prevented. Thus, the rubber should be able to easily flow and fill in the grooves, holes, and/or corners of the mould, if any. Still further, the wear indicator itself should not deteriorate the driving properties of the tyre. Moreover, the wear indicator should be small compared to the tyre tread patterns in order not to deteriorate the driving properties of the tyre.